t <- 0:255
s1 <- 20*sin(2*pi*t/256)
s2 <- 50*sin(2*pi*3*t/256)
s3 <- 7*rnorm(256)

fft1 <- fft(s1+s2+s3)
f1 <- c(rep(1,10),rep(0,236),rep(1,10))

plot(Re(fft(fft1*f1,inverse = TRUE))/length(t), type="l")
